Vehicle wheel bearing apparatus is adapted to freely rotatably support a wheel hub to mount a wheel via a rolling bearing. An inner ring rotation type is used for driving wheels and both inner ring rotation and outer ring rotation types are used for driven wheels. Double row angular ball bearings are widely used in such a bearing apparatus since it has a desirable bearing rigidity, high durability against misalignment, and small rotation torque required for fuel consumption. On the contrary double row tapered roller bearings are widely used for off-road vehicles, trucks and heavy duty vehicles.
The vehicle wheel bearing apparatus is broadly classified into a first, second, third or fourth generation structure. A first generation structure includes a wheel bearing with a double row angular contact ball bearing fit between a knuckle, forming part of a suspension, and a wheel hub. The second generation structure includes a body mounting flange or a wheel mounting flange directly formed on the outer circumferential surface of an outer member. The third generation structure includes one of the inner raceway surfaces directly formed on the outer circumferential surface of the wheel hub. The fourth generation structure includes the inner raceway surfaces directly formed on the outer circumferential surfaces of the wheel hub and the constant velocity universal joint.
One example of a prior art wheel bearing apparatus is shown in FIG. 3. The vehicle wheel bearing apparatus 50 is formed by a double row tapered roller bearing having an outer member 51 integrally formed on its outer circumferential surface with a body mounting flange 51b. The flange 51b is to be mounted on a knuckle (not shown) of a vehicle. The outer member inner circumferential surface is formed with double row outer raceway surfaces 51a, 51a. An inner member is integrally formed on its outer circumferential surface with double row inner raceway surfaces 52a, 54a, opposite to the double row outer raceway surfaces 51a, 51a. Double row tapered rollers 56, 56 are freely rollably contained between the outer raceway surfaces 51a, 51a and inner raceway surfaces 52a, 54a. Cages 57, 57 freely rollably hold the double row tapered rollers 56, 56.
The inner member 55 includes a wheel hub 52 with a wheel mounting flange 53 integrally formed at one end. One inner raceway surface 52a is formed on the outer circumferential surface. A cylindrical portion 52b axially extends from the inner raceway surface 52a. An inner ring 54 is press fit onto the cylindrical portion 52b. The inner ring 54 is formed on its outer circumferential surface with the other inner raceway surface 54a. Thus, the inner member 55 forms the wheel bearing apparatus of the third generation structure for driving a driving wheel.
In addition, hub bolts 60 are adapted to be mounted on the wheel mounting flange 53 equidistantly along its outer periphery. Furthermore, seals 58, 59 are mounted in annular openings formed between the outer member 51 and the inner member 55. The seals prevent the leakage of grease contained within the bearing apparatus. Additionally, they prevent entry, from the outside, of rain water or dusts into the bearing apparatus.
In such a wheel bearing apparatus, radially extending ribs 61 are formed on a surface of the inner side of the wheel mounting flange 53. The ribs 62 are positioned at the hub bolts 60, as shown in FIG. 4, to increase the rigidity of the wheel bearing apparatus. Recesses 62, each having a substantially circular arc, are formed on the outermost periphery of the wheel mounting flange 53 between the hub bolts 60 to reduce the weight of the wheel bearing apparatus. On the other hand, the body mounting flange 51b of the outer member 51 is formed with apertures 63 for bolts fastened to a knuckle (not shown). The flange 51b is formed with recesses 64 each having a smoothly curved configuration on its outermost periphery between the bolt apertures 64. Each recess 64 is formed radially inward beyond the pitch circular diameter of the bolt apertures 63 in order to remove excessive material of the body mounting flange 51b (see Japanese Laid-open Patent Publication No. 65049/2000).